topic EOS R5 Slow Card Write Speed Error - Please help in EOS DSLR & Mirrorless Cameras

EOS R5 Slow Card Write Speed Error - Please help

Davidw3 — Mon, 26 May 2025 22:30:20 GMT

When I record with high frame rate (119.9 fps, 4K-U0 for slow motion purposes, after about 3 seconds the recording stops and says "Slow Card Write Speed". I have a CF Express SanDisk Extreme Pro Card with Read 1700 MB/s Read and 1200 MB/s Write. Do I need something faster than that (what do I need?) or is there a setting I need to change in the camera?

Thanks

Re: EOS R5 Slow Card Write Speed Error - Please help

rs-eos — Mon, 26 May 2025 22:47:22 GMT

The only value to pay attention to is the sustained write speed. I just tried finding that value for a SanDisk CFexpress card and came up empty. Side note: this is the main reason I stopped using SanDisk cards as they don't always publish the most important metrics.

From the User Manual, it looks like the max bit rate for 119.88 fps footage would be 1880 Mbps or around 235 MBps, so that should be within a sustained write speed (for reference, an Angelbird CFexpress 2.0 type B card has a sustained write of 800 MBps).

Other things to check:

Did you format the card before use? A fragmented card can lead to slower writes.
Did the camera experience any temperature warnings while recording? Writes could end up being slower to prevent overheating.

Re: EOS R5 Slow Card Write Speed Error - Please help

Peter — Mon, 26 May 2025 23:10:33 GMT

Does low level format exists for CF Express in your camera?

Re: EOS R5 Slow Card Write Speed Error - Please help

Davidw3 — Mon, 26 May 2025 23:55:09 GMT

Thanks for the info.
I did format the card in-camera and no temp issues. I get the same error whether I just turned on the camera or if I have been using it for a while. I am thinking I will try something other than SanDisk and see if that works.